Advanced formation testing tools have been used for example to capture fluid samples from subsurface earth formations. The fluid samples could be gas, liquid hydrocarbons or formation water. Formation testing tools are typically equipped with a device, such as a straddle or dual packer. Straddle or dual packers comprise two inflatable sleeves around the formation testing tool, which makes contact with the earth formation in drilled wells when inflated and seal an interval of the wellbore. The testing tool usually comprises a port and a flow line communicating with the sealed interval, in which fluid is flown between the packer interval and in the testing tool.
Examples of such tools are schematically depicted in FIGS. 1A to 1D. FIG. 1A shows an elevational view of a typical drill-string conveyed testing tool 10a. Testing tool 10a is conveyed by drill string 13a into wellbore 11 penetrating a subterranean formation 12. Drill string 13a has a central passageway that usually allows for mud circulation from the surface, then through downhole tool 10a, through the drilling bit 20 and back to the surface, as known in the art. Testing tool 10a may be integral to one of more drill collar(s) constituting the bottom hole assembly or “BHA”. Testing tool 10a is conveyed among (or may itself) one or more measurement-while-drilling or logging while drilling tool(s) known to those skilled in the art. In some cases, the bottom hole assembly is adapted to convey a casing or a liner during drilling. Optionally, drill string 13a allows for two-way mud pulse telemetry between testing tool 10a and the surface. A mud pulse telemetry system typically comprises surface pressure sensors and actuators (such as variable rate pumps) and downhole pressure sensors and actuators (such as a siren) for sending acoustic signals between the downhole tool and the surface. These signals are usually encoded, for example compressed, and decoded by surface and downhole controllers. Alternatively any kind of telemetry known in the art may be used instead of mud pulse telemetry, such as electromagnetic telemetry or wired drill pipe telemetry. Tool 10a may be equipped with one or more packer(s) 26a, that are preferably deflated and maintained below the outer surface of tool 10a during drilling operations. When testing is desired, a command may be sent from the surface to the tool 10a via the telemetry system. Straddle packer 26a can be inflated and extended toward the wall of wellbore 11, achieving thereby a fluid connection between the formation 12 and the testing tool 10a across wellbore 11. As an example, tool 10a may be capable of drawing fluid from formation 12 into the testing tool 10a, as shown by arrows 30a. Usually one or more sensor(s) located in tool 10a, such as pressure sensor, monitors a characteristic of the fluid. The signal of such sensor may be stored in downhole memory, processed or compressed by a downhole processor and/or send uphole via telemetry. Note that in some cases, part of tool 10a may be retrievable if the bottom hole assembly becomes stuck in the wellbore, for example by lowering a wireline cable and a fishing head.
FIG. 1B shows an elevational view of a typical drill-stem conveyed testing tool 10b. Testing tool 10b is conveyed by tubing string 13b into wellbore 11 penetrating a subterranean formation 12. Tubing string 13b may have a central passageway that usually allows for fluid circulation (wellbore fluids or mud, treatment fluids, or formation fluids for example). The passageway may extend through downhole tool 10b, as known in the art. Tubing string 13b may also allow for tool rotation from the surface. Testing tool 10b may be integral to one of more tubular(s) screwed together. Testing tool 10b is conveyed among (or may be itself) one or more well testing tool(s) known to those skilled in the art, such as perforating gun. The testing tool 10b may be lowered in an open hole as shown, or in a cased wellbore. In some cases, tubing string 13b allows for two-way acoustic telemetry between testing tool 10b and the surface, or any kind of telemetry known in the art may be used instead. Tool 10b may be equipped with one or more packer(s) 26b that is usually retracted (deflated) during tripping of testing tool 10b. When testing is desired, tool 10b may be set into testing configuration, for example by manipulating flow in tubing string 13b. Extendable packer 26b can be extended (inflated) toward the wall of wellbore 11, achieving thereby a fluid connection between an interval of formation 12 and the testing tool 10b across wellbore 11. As an example, tool 10b may be capable of drawing fluid from formation 12 into the testing tool 10b, as shown by arrows 30b. Usually one or more sensor(s) located in tool 10b, such as pressure or flow rate sensor, monitor(s) a characteristic of the fluid. The signal of such sensor may be stored in downhole memory, processed or compressed by a downhole processor and/or send uphole via telemetry. Note that in some cases part of tool 10b may be a wireline run-in tool, lowered for example into the tubing string 13b when a test is desired.
FIG. 1C shows an elevational view of a typical wireline conveyed testing tool 10c. Testing tool 10c is conveyed by wireline cable 13c into wellbore 11 penetrating a subterranean formation 12. Testing tool 10c may be an integral tool or may be build in a modular fashion, as known to those skilled in the art. Testing tool 10c is conveyed among (or may itself) one or more logging tool(s) known to those skilled in the art. Preferably the wireline cable 13c allows signal and power communication between the surface and testing tool 10c. Testing tool 10c may be equipped with straddle packers 26c, that are preferably recessed below the outer surface of tool 10c during tripping operations. When testing is desired, straddle packer 26c can be extended (inflated) toward the wall of wellbore 11 achieving, thereby, a fluid connection between an interval of formation 12 and the testing tool 10b across wellbore 11. As an example, tool 10c may be capable of drawing fluid from formation 12 into the testing tool 10c, as shown by arrows 30c. Examples of such tools can be found U.S. Pat. No. 4,860,581 and U.S. Pat. No. 4,936,139, both assigned to the assignee of the present invention, and incorporated herein by reference. Note in some cases that wireline tools (and wireline cable) may be alternatively conveyed on a tubing string, or by a downhole tractor (not shown). Note also that the wireline tool may also be used in run-in tools inside a drill string, such as the drill string shown in FIG. 1a. In these cases, the wireline tool 10c usually sticks out of bit 20 and may perform measurements, for example when the bottom hole assembly is pulled out of wellbore 11.
FIG. 1D shows an elevational view of another typical wireline conveyed testing tool 10d. Testing tool 10d is conveyed by wireline cable 13d into wellbore 11 penetrating a subterranean formation 12. This time wellbore 11 is cased with a casing 40. Testing tool 10d may be equipped with one or more extendable (inflatable) packer(s) 26d, that are preferably recessed (deflated) below the outer surface of tool 10d during tripping operations. Tool 10d is capable of perforating the casing 40, usually below at least one packer (see perforation 41), for example, the tool could include one or more perforating gun(s). In FIG. 1D, the testing tool 10d is shown drawing fluid from formation 12 into the testing tool 10d (see arrows 30d). Usually one or more sensor(s) is located in tool 10d, such as a pressure sensor, monitors a characteristic of the fluid. The signal of such sensor is usually send uphole via telemetry. Note that in some cases, tools designed to test a formation behind a casing may also be used in open hole. Note also that cased formations may be evaluated by downhole tool conveyed by other means than wireline cables.
Typical tools are not restricted to two packers. Downhole systems having more than two packers have been disclosed for example in U.S. Pat. No. 4,353,249, U.S. Pat. No. 4,392,376, U.S. Pat. No. 6,301,959 or U.S. Pat. No. 6,065,544.
In some situations, a problem occurs when fluid is drawn into the tool through openings along the tool body. Formation fluids, wellbore fluids and other debris from the wellbore may occupy the volume between the upper sealed packer and the lower sealed packer. This causes various fluids to enter the same openings (or similar openings) located in the sealed volume. Moreover, when the density of the wellbore fluid is larger than the density of the formation fluid, it is very difficult to remove all of the wellbore fluid since there will be a residual of wellbore fluid that resides between the lowest opening and the lowest packer, even after a long pumping time. Thus, these wellbore fluids can contaminate the formation fluid entering the tool.
Downhole systems facilitating the adjustment of the flow pattern between the formation and the interior of the tool have been disclosed for example in patent application US 2005/0155760. These systems may be used to reduce the contamination of the formation fluid by mud filtrate surrounding the wellbore. Note that methods applicable for reducing the contamination by mud filtrate surrounding the wellbore are not always applicable for reducing the contamination by fluids and other debris from the wellbore.
Despite the advances in formation testing, there is a need for improved testing methods utilizing a tool having a plurality of packers spaced apart along the axis of the tool, and at least a port on the tool body located between two packer elements. Such methods are preferably capable of reducing the contamination of the formation fluid by fluid or debris in the wellbore. These methods may comprise adjusting in situ the length of a sealed interval between two packer elements. Alternatively, these methods may comprise adjusting the location of the port within a packer interval.